Radio frequency (RF) phased arrays are widely used for both government and commercial systems. The array of antennas creates a steerable beam of RF waves that may be electronically controlled to point in different directions without having to physically move the antennas. By way of example, RF phased array systems may be used in numerous applications such as radars, acoustic/sonar, imaging, seismology, etc.
Optical phased array devices are similar to RF phased arrays in that they provide for an electronically steerable beam, but in optical phased arrays the beam is made up of light waves instead of RF signals. Yet, a significant challenge of optical phased arrays is size constraints. That is, because of the wavelengths of light involved, the requisite spacing between optical emitters is relatively small (i.e., microscopic). As a result, there are significant fabrication challenges to implementing relatively large scale optical phased array devices.
One example optical phase array configuration is set forth in U.S. Pat. No. 8,988,754 to Sun et al. This patent discloses an optical phased array formed of a large number of nanophotonic antenna elements, which may be used to project complex images into the far field. These nanophotonic phased arrays, including the nanophotonic antenna elements and waveguides, are formed on a single chip of silicon using complementary metal-oxide-semiconductor (CMOS) processes. Directional couplers evanescently couple light from the waveguides to the nanophotonic antenna elements, which emit the light as beams with phases and amplitudes selected so that the emitted beams interfere in the far field to produce the desired pattern. In some cases, each antenna in the phased array may be optically coupled to a corresponding variable delay line, such as a thermo-optically tuned waveguide or a liquid-filled cell, which are used to vary the phase of the antenna's output (and the resulting far-field interference pattern).
Another example configuration is set forth in Guan et al., “Hybrid 3D Photonic Integrated Circuit for Optical Phased Array Beam Steering,” CLEO, 2015. This reference discloses a hybrid integrated optical phased array (OPA) based on a 2D photonic integrated circuit and 3D waveguides. The 4×4 OPA supports 4.93° horizontal and vertical beam steering near 1550 nm with 7.1 dB loss.
Despite the existence of such systems, further developments in optical phased array devices may be desirable in certain applications.